A flange portion is provided to at least a part of the periphery at the center position in the direction of the optical axis of a lens. The lens is held with clamping members and a lens holding metallic part, with the flange portion pressed by the clamping members. The portion where the flange portion is provided, suffers no compressive strain and tensile strain due to the bending of the lens, and is a part of the periphery of a neutral plane, which is the farthest plane from the optical surface of the lens. Therefore, the influence of the clamping force on the flange portion acting on other portions of the lens is reduced to the utmost, and the deformation of the optical surface due to the force acting on the flange portion is reduced to a minimum. As a result, the deterioration of the optical properties of the lens can be suppressed to the utmost.